Secondary batteries

Abstract

To provide a secondary battery that can improve output when starting an electric mobile body.SOLUTION: A secondary battery 2 has a positive electrode 4 and a negative electrode 5. The positive electrode 4 has a first active material 41 and a second active material 42. The first active material 41 is a lithium nickel cobalt manganese oxide. The second active material 42 is lithium iron manganese phosphate. In addition, the average particle size of the first active material 41 is larger than the average particle size of the second active material 42.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention ,two Next train In the pond Regarding. [Background technology]

[0002] Patent Document 1 discloses an electric flying object equipped with multiple secondary batteries. This electric flying object is configured to perform an emergency evacuation operation if an abnormality occurs in one of the secondary batteries. Furthermore, when an abnormality occurs in one secondary battery, this electric flying object secures the output necessary for flight by using other secondary batteries to compensate, thereby preventing the development of a problem that could compromise safety. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2020-196440 Summary of the Invention [Problem to be solved by the invention]

[0004] However, electric aircraft generally require a relatively high output when starting up and taking off. Therefore, when an electric aircraft takes off, the discharge rate of the secondary battery increases, which can easily cause imbalances in the ion concentration distribution in the secondary battery. This imbalance in the ion concentration distribution can cause temporary degradation, which is a temporary increase in the internal resistance of the secondary battery. Therefore, even if the electric aircraft described in Patent Document 1 is equipped with multiple secondary batteries, temporary degradation can occur in all of the multiple secondary batteries. Therefore, there is room for further improvement in terms of ensuring output power at the time of starting an electric aircraft.

[0005] The present invention has been made in view of the above problem, and is capable of improving the output at the start of an electric vehicle. Ru2 Next train The pondIt is what we intend to provide. [Means for solving the problem]

[0007] A first aspect of the present invention is a secondary battery (2) having a positive electrode (4) and a negative electrode (5), the positive electrode comprises a first active material (41) and a second active material (42); The first active material is a lithium nickel cobalt manganese oxide represented by the following formula (1), and the second active material is lithium manganese iron phosphate, the average particle size of the first active material is larger than the average particle size of the second active material; The secondary battery is mounted on an electric flying object (100), In the following formula (1), x+y+z=1, 0.6≦x<1. the law of nature , The secondary battery further comprises a solid electrolyte, The solid electrolyte is an oxide-based solid electrolyte having a pyrochlore structure and containing at least lithium, lanthanum, niobium, oxygen, and fluorine. It is in a secondary battery. LiNi x Co y Mn z O2···(1) A second aspect of the present invention is a secondary battery (2) having a positive electrode (4) and a negative electrode (5), the positive electrode comprises a first active material (41) and a second active material (42); The first active material is lithium nickel cobalt manganese oxide, and the second active material is lithium manganese iron phosphate represented by the following formula (3): the average particle size of the first active material is larger than the average particle size of the second active material; The secondary battery is mounted on an electric flying object (100), In the following formula (3), 0.5 <x≦0.6であ the law of nature , The secondary battery further comprises a solid electrolyte, The solid electrolyte is an oxide-based solid electrolyte having a pyrochlore structure and containing at least lithium, lanthanum, niobium, oxygen, and fluorine. It is in a secondary battery. LiMn x Fe 1-x PO4···(3) As a reference aspect, a secondary battery (2) is mounted on an electric flying object (100) and has a positive electrode (4) and a negative electrode (5), the positive electrode comprises a first active material (41) and a second active material (42) having a higher resistance than the first active material when the secondary battery has a predetermined SOC value; There is a secondary battery in which the first active material is a lithium nickel cobalt manganese oxide having a layered rock salt structure, and the second active material is lithium manganese iron phosphate having an olivine structure. [Effects of the Invention]

[0011] The above reference mode The secondary battery includes a first active material and a second active material that has a higher resistance than the first active material when the secondary battery has a predetermined SOC value. The first active material is a lithium nickel cobalt manganese oxide having a layered rock salt structure, and the second active material is a lithium manganese iron phosphate having an olivine structure. This suppresses temporary degradation of the secondary battery during startup, ensuring high output from the secondary battery. As a result, the output of an electric vehicle during startup can be improved.

[0014] As described above, according to the above aspect, it is possible to improve the output at the start of the electric vehicle. Ru2 Next train The pond can be provided. In addition, the symbols in parentheses described in the claims and the means for solving the problems indicate the correspondence with the specific means described in the embodiments described below, and do not limit the technical scope of the present invention. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is an external view of an electric flying object equipped with a battery system according to a first embodiment. [Figure 2] 1 is a cross-sectional view of a secondary battery according to a first embodiment. [Figure 3] 4 is a graph showing the relationship between the SOC and voltage of the secondary battery in the first embodiment. [Figure 4] 10 is a graph showing the relationship between the SOC and voltage of a secondary battery in Comparative Example 1. [Figure 5] 10 is a graph showing the relationship between the SOC and voltage of a secondary battery in Comparative Example 2. [Figure 6] 4 is a flowchart showing a flow from charging a secondary battery to discharging during normal operation in the first embodiment. [Figure 7] 6 is a graph showing the magnitude of output during takeoff, normal operation, and landing in the first embodiment. [Figure 8] 4 is a graph showing the relationship between the discharge rate, the temperature of the secondary battery, and the internal resistance of the secondary battery in the first embodiment and the first comparative example. [Figure 9] 3 is a scanning electron microscope photograph of a cross section of a secondary battery in Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0016] (Embodiment 1) Embodiments of a battery system, a secondary battery, and an electric flying object will be described with reference to FIGS. As shown in Fig. 1, a battery system 1 of this embodiment is mounted on an electric vehicle 10. The battery system 1 has a secondary battery 2 and a battery control unit 3 that controls the discharge of the secondary battery 2. The battery control unit 3 controls the secondary battery 2 to perform high-rate discharge when the electric vehicle 10 starts. The high-rate discharge is discharge at a rate higher than the discharge rate of the secondary battery 2 during normal operation of the electric vehicle 10.

[0017] 2, the positive electrode 4 of the secondary battery 2 includes a first active material 41 and a second active material 42. The second active material 42 has a high resistance region where the resistance is higher than that of the first active material 41 in a high-rate discharge region, which is a State Of Charge (SOC) region of the secondary battery 2 where high-rate discharge is performed at startup.

[0018] The secondary battery 2 is configured such that, when high-rate discharge is performed at startup, the utilization rate of the second active material 42 becomes higher than the utilization rate of the first active material 41, and then the utilization rate of the first active material 41 becomes higher than the utilization rate of the second active material 42. In this embodiment, the high-rate discharge region can be, for example, a region from an initial SOC value, which is the SOC value of the secondary battery 2 when high-rate discharge begins, to an SOC value that is 20% points lower than the initial SOC value at startup. That is, for example, if the initial SOC value is 90%, the high-rate discharge region can be an SOC region where the SOC value is in the range of 70 to 90%. Then, high-rate discharge can be performed continuously in the SOC region where the SOC value is in the range of 70 to 90%, for example.

[0019] The battery system 1 of this embodiment can be mounted on, for example, an electric vehicle 10 and used as a means for controlling discharge when the electric vehicle 10 moves. The electric vehicle 10 can be, for example, an electric flying vehicle 100 such as an electronic vertical take-off and landing aircraft (eVTOL), an electronic short distance take-off and landing aircraft (eSTOL), or a drone. In this embodiment, the electric vehicle 10 is an electric vertical take-off and landing aircraft of the electric flying vehicle 100.

[0020] As shown in Fig. 1, the electric flying object 100 includes a battery system 1. That is, the electric flying object 100 includes a secondary battery 2. The secondary battery 2 stores power to drive a motor (not shown) and other components mounted on the electric flying object 100. In this embodiment, the secondary battery 2 is a lithium-ion battery.

[0021] As shown in Fig. 2, the secondary battery 2 mounted on the electric flying object 100 has a positive electrode 4 and a negative electrode 5. The positive electrode 4 and the negative electrode 5 have current collectors 43 and 52, respectively. By electrically connecting a load or a power generation device to these current collectors 43 and 52, the secondary battery 2 can be discharged or charged. The current collectors 43 and 52 can be made of a conductor such as a metal foil or a metal plate.

[0022] The secondary battery 2 has a separator 6. The separator 6 is disposed between the positive electrode 4 and the negative electrode 5, separating the positive electrode 4 from the negative electrode 5. The separator 6 is permeable to lithium ions. In this embodiment, the separator 6 is in a sheet shape and has a porous structure. The separator may be made of, for example, a polyolefin such as polyethylene or polypropylene.

[0023] The secondary battery 2 includes an electrolyte 20. In this embodiment, the electrolyte 20 is impregnated into the positive electrode 4, the negative electrode 5, and the separator 6. The electrolyte 20 may contain, for example, a non-aqueous solvent and a lithium salt. The non-aqueous solvent may be, for example, dimethyl carbonate, ethyl methyl carbonate, ethylene carbonate, or a mixture thereof. The lithium salt may be, for example, LiPF6, LiBF4, LiClO4, or a mixture thereof. The electrolyte 20 may also contain, for example, vinylene carbonate as an additive.

[0024] A solid electrolyte can also be used as the electrolyte 20 of the secondary battery 2. The solid electrolyte can be, for example, a polymer-based solid electrolyte such as polyethylene oxide, a sulfide-based solid electrolyte, or an oxide-based solid electrolyte. The sulfide-based solid electrolyte can be, for example, a solid electrolyte having an argyrodite structure such as Li6PS5Cl, or Li 10 GeP2S 12 As the oxide-based solid electrolyte, for example, Li 1.25 La 0.58Solid electrolytes with pyrochlore structure such as Nb2O6F, Li7La3Zr2O 12 Solid electrolytes with garnet structure such as Li 1.4 A l0.4 Ti 1.6 Solid electrolytes with NASICON-type structure such as (PO4)3, La 0.57 Li 0.29 A solid electrolyte having a perovskite structure such as TiO3 can be used. The electrolyte 20 can also be a mixture of two or more of the solid electrolytes listed above. The solid electrolytes listed above can also be contained in the positive electrode 4 and the negative electrode 5.

[0025] The positive electrode 4 and the negative electrode 5 are provided on the surfaces of current collectors 43 and 52, respectively, and have active material layers 40 and 50 containing an active material. The active material layers 40 and 50 can contain, in addition to the active material, for example, a conductive material, a binder, etc.

[0026] As the active material 51 contained in the active material layer 50 of the negative electrode 5, for example, graphite, silicon, lithium metal, or LTO (lithium titanate) based active material can be used.

[0027] The active material layer 40 of the positive electrode 4 includes a first active material 41 and a second active material 42. In this embodiment, the first active material 41 is a lithium nickel cobalt manganese oxide having a layered rock salt structure. The second active material 42 is lithium manganese iron phosphate having an olivine structure. The lithium nickel cobalt manganese oxide serving as the first active material 41 has a higher energy density than the lithium manganese iron phosphate serving as the second active material 42. Note that the active material layer 40 of the positive electrode 4 may also contain, for example, active materials other than the first active material 41 and the second active material 42.

[0028] In this embodiment, the resistance of the first active material 41 decreases as the SOC of the secondary battery 2 increases. The lithium nickel cobalt manganese oxide that is the first active material 41 can be expressed by the following formula (1). The lithium nickel cobalt manganese oxide that is the first active material 41 can be expressed by the following formula (2). In the following formula (1), x + y + z = 1, 0.6 ≦ x < 1, 0.02 ≦ y ≦ 0.2, and 0.02 ≦ z ≦ 0.2. LiNi x Co y Mn z O2···(1) LiNi 0.8 Co 0.1 Mn 0.1 O2···(2)

[0029] The second active material 42 has a higher resistance than the first active material 41 when the SOC value of the secondary battery 2 is a predetermined value. In other words, as described above, the second active material 42 has a high resistance region in which the resistance is higher than that of the first active material 41 in a high rate discharge region. The lithium manganese iron phosphate of the second active material 42 can be expressed by the following formula (3). In this embodiment, the lithium manganese iron phosphate of the second active material 42 can be expressed by the following formula (4). In addition, in the following formula (3), x>0.5. LiMn x Fe 1-x PO4···(3) LiMn 0.6 Fe 0.4 PO4···(4)

[0030] The proportion of the first active material 41 relative to the total active materials of the positive electrode 4 is 50 to 95 wt %, and the proportion of the second active material 42 relative to the total active materials of the positive electrode 4 is 5 to 50 wt %. When the initial SOC value is set to a relatively high value of approximately 90%, the proportion of the second active material 42 relative to the total active materials of the positive electrode 4 is preferably 5 to 20 wt %, and the proportion of the first active material 41 relative to the total active materials of the positive electrode 4 is preferably 80 to 95 wt %. The proportion of the first active material 41 relative to the total active materials of the positive electrode 4 is more preferably 90 wt % or more, and the proportion of the second active material 42 relative to the total active materials of the positive electrode 4 is more preferably 10 wt % or less. The proportion of the second active material 42 relative to the total active materials of the positive electrode 4 is even more preferably 9 wt % or less. Furthermore, when the starting SOC value is set to a relatively low value of about 60%, the ratio of the second active material 42 to the total active material of the positive electrode 4 is preferably 40 to 50% by weight, and the ratio of the first active material 41 to the total active material of the positive electrode 4 is preferably 50 to 60% by weight.

[0031] In this embodiment, the average particle diameter of the first active material 41 is larger than the average particle diameter of the second active material 42. In other words, the average particle diameter of the second active material 42 is smaller than the average particle diameter of the first active material 41. However, whether the average particle diameter of the first active material 41 is larger than the average particle diameter of the second active material 42 or whether the average particle diameter of the first active material 41 is smaller than the average particle diameter of the second active material 42, the output at the start of the electric vehicle 10 can be improved. The average particle diameter of the first active material 41 can be, for example, 5 to 15 μm, and the average particle diameter of the second active material 42 can be, for example, 0.1 to 20.0 μm.

[0032] Next, the characteristics of the secondary battery 2 of this embodiment will be described. As shown in FIG. 3 , the voltage of the secondary battery 2 of this embodiment changes with changes in the SOC value. Specifically, the smaller the SOC value of the secondary battery 2, the smaller the voltage of the secondary battery 2, which is the potential difference between the positive electrode 4 and the negative electrode 5. As will be described later, the utilization rates of the first active material 41 and the second active material 42 vary depending on the voltage of the secondary battery 2. In this embodiment, the utilization rate of the first active material 41 refers to the ratio of lithium ions absorbed by the first active material 41 to all lithium ions absorbed by the active material of the positive electrode 4 during discharge. The utilization rate of the second active material 42 refers to the ratio of lithium ions absorbed by the second active material 42 to all lithium ions absorbed by the active material of the positive electrode 4 during discharge.

[0033] In this embodiment, the Fe (i.e., iron) of the lithium manganese iron phosphate (LMN) of the second active material 42 is primarily involved in the charge / discharge reactions around 3.4 V. Furthermore, the Mn (i.e., manganese) of the lithium manganese iron phosphate (LMN) of the second active material 42 is primarily involved in the charge / discharge reactions around 4.0 V. Therefore, as shown in FIG. 5 , the secondary battery of Comparative Embodiment 2, which has only lithium manganese iron phosphate as the positive electrode active material, exhibits flat voltage curves around 3.4 V and 4.0 V, and is primarily charged and discharged in potential regions around 3.4 V and 4.0 V. That is, in this embodiment, the second active material 42 primarily undergoes charge / discharge reactions in potential regions around 3.4 V and 4.0 V. Therefore, in this embodiment, as shown in FIG. 3 , when the voltage of the secondary battery 2 is around 3.4 V and 4.0 V, a second high utilization region is present, in which the utilization rate of the second active material 42 is higher than that of the first active material 41. Furthermore, the secondary battery 2 is in a second high utilization region when its SOC value is around 10% and between 80% and 90%. In these second high utilization regions, the second active material 42 is mainly involved in the reactions during charging and discharging. In other words, the secondary battery 2 is configured to have the second high utilization region in a low SOC region where the SOC value of the secondary battery 2 is lower than a predetermined value. The low SOC region can be, for example, a region where the SOC value is 30% or less. An SOC of 0% means that the secondary battery 2 is fully discharged, and an SOC of 100% means that the secondary battery 2 is fully charged.

[0034] In this embodiment, as shown in Fig. 3, the regions other than the two second high utilization regions are first high utilization regions in which the utilization rate of first active material 41 is higher than the utilization rate of second active material 42. In the first high utilization region, first active material 41 is mainly utilized for reactions during charging and discharging. Note that, as shown in Fig. 4, in the case of a secondary battery of Comparative Embodiment 1 in which only lithium nickel cobalt manganese oxide, the same as the first active material, is used as the positive electrode active material, the voltage curve shows a decrease in the voltage as the SOC value decreases.

[0035] The first active material 41 and the second active material 42 have different resistances. The internal resistance of the secondary battery 2 and the resistance of the active materials vary depending on the state of charge (SOC) of the secondary battery 2. In this embodiment, the second active material 42 has a lower resistance than the first active material 41 in the low SOC region. The first active material 41 has a higher resistance in the low SOC region than in other SOC regions. Therefore, as shown in FIG. 4, Comparative Embodiment 1 also has a higher internal resistance in the low SOC region than in other SOC regions.

[0036] In this embodiment, the second active material 42 has a high resistance region in which the resistance is higher than that of the first active material 41 in a high-rate discharge region where the SOC value is in the range of 70 to 90%. Here, the magnitude of the resistance of the first active material 41 and the second active material 42 can be measured, for example, by DCIR (Direct Current Internal Resistance) measurement, which measures the DC resistance at each SOC value of the secondary battery 2, or by AC impedance measurement, which measures the AC resistance at each SOC value of the secondary battery 2. Whether the internal resistance of the secondary battery 2 measured by these measurement methods is due to the first active material 41 or the second active material 42 can be determined based on a secondary battery using only the same active material as either the first active material or the second active material as the positive electrode active material. Specifically, the magnitude of the resistance of the first active material 41 and the second active material 42 can be determined by referring to the SOC-OCV (Open Circuit Voltage) curves or SOC-CCV (Closed Circuit Voltage) curves of a secondary battery using only the same active material as the first active material as the positive electrode active material and a secondary battery using only the same active material as the second active material as the positive electrode active material, and the internal resistance at each SOC. For example, the magnitude of the resistance of the second active material 42 in the secondary battery 2 of this embodiment can be determined by referring to the graph of Comparative Example 2 in FIG. 5, which has a flat voltage curve near 4.0 V, and the graph of Comparative Example 1 in FIG. 4, which does not have a flat voltage curve near 4.0 V. That is, as shown in the graph of FIG. 3, it can be determined that the internal resistance of the secondary battery 2 in the second high utilization region where the SOC value is near 80% and the voltage is near 4.0 V is mainly due to the resistance of the second active material 42 by referring to the graph of Comparative Example 1 in FIG. 4 and the graph of Comparative Example 2 in FIG. 5.

[0037] Next, the electric flying object 100 of this embodiment will be described. As shown in Fig. 1, the electric flying vehicle 100 of this embodiment has a main body 102, fixed wings, and rotors 101. The main body 102 can be provided with, for example, a storage space for storing cargo to be transported. In this embodiment, the electric flying vehicle 100 has main wings 103 and tail wings 104 as fixed wings for generating lift. The electric flying vehicle 100 can be, for example, a manned or unmanned aircraft.

[0038] The electric flying object 100 also includes a plurality of rotors 101 and a plurality of motors (not shown) that rotate each of the rotors 101. The motors are driven by power from the secondary battery 2. In this embodiment, the rotors 101 are provided on the main body 102 and the main wing 103. Rotating the rotors 101 with the motors generates lift and thrust, allowing the electric flying object 100 to fly.

[0039] The electric flying body 100 is configured to be able to move in a direction along the vertical direction and in a horizontal direction. The electric flying body 100 is also configured to be able to move in a direction that includes a component along the vertical direction and a component along the horizontal direction, that is, to move in a direction inclined relative to the horizontal direction.

[0040] The electric flying object 100 of this embodiment is equipped with a plurality of secondary batteries 2. The secondary batteries 2 can be connected to each other in series or parallel, for example. In this embodiment, the electric flying object 100 is equipped with a battery module in which the secondary batteries 2 are modularized by connecting them in series and parallel.

[0041] The electric flying body 100 of this embodiment has an air vehicle control unit 105 that controls the flight of the electric flying body 100. The air vehicle control unit 105 can include, for example, a processor, a memory, a communication circuit for wireless communication, and the like. The processor can control operations such as takeoff and landing and normal operation of the electric flying body 100 by, for example, executing a control program pre-stored in the memory. Furthermore, the takeoff and landing and normal operation of the electric flying body 100 can be performed based on, for example, preset flight path information, or can also be performed based on commands from outside the electric flying body 100.

[0042] In the battery system 1 mounted on the electric flying object 100, the battery control unit 3 includes a processor and a memory. The processor of the battery control unit 3 can control the discharge of the secondary battery 2, for example, by executing a control program pre-stored in the memory. In this embodiment, the battery system 1 is also part of the flying object control unit 105.

[0043] Next, the flow from charging the electric flying object 100 to performing normal operation will be described with reference to the flowchart in FIG. First, in step S1, the secondary battery 2 mounted on the electric flying body 100 is charged to ensure a sufficient cruising distance for the electric flying body 100. In this embodiment, the secondary battery 2 is charged using an external charging facility (not shown). In this embodiment, charging continues until the SOC of the secondary battery 2 reaches 90%. After that, in step S2, charging and discharging of the secondary battery 2 is paused until the electric flying body 100 starts flying. Note that after charging the secondary battery 2, the electric flying body 100 can also start flying immediately without pausing.

[0044] Next, in step S3, the electric flying object 100 is started, and high-rate discharge of the secondary battery 2 is initiated. At start-up, the electric flying object 100 of this embodiment takes off by driving the rotor 101 and reaches a predetermined altitude. Therefore, as shown in FIG. 7, the electric flying object 100 requires a higher output when taking off at start-up compared to normal operation. Therefore, the battery control unit 3 controls high-rate discharge of the secondary battery 2, driving the motor at high output and rotating the rotor 101. In this embodiment, high-rate discharge is performed at a discharge rate of, for example, 4 to 12 C (Capacity). In this embodiment, high-rate discharge begins when the SOC of the secondary battery 2 is 80% or higher. In this embodiment, normal operation refers to the cruising of the electric flying object 100 from immediately after take-off and reaching a predetermined altitude (i.e., the normal operation start point described below) until it reaches the sky above its destination. That is, normal operation is movement of the electric flying body 100 that does not include takeoff and landing. Also, takeoff and landing of the electric flying body 100 are mainly movement along the vertical direction.

[0045] Next, in step S4 of Fig. 6, the secondary battery 2 generates heat by performing high-rate discharge. In this heat generation step of step S4, the temperature of the secondary battery 2 can be increased to, for example, 45°C or higher. Specifically, in the heat generation step of step S4, high-rate discharge is performed in the high resistance region and the second high utilization region, causing the secondary battery 2 to generate heat. In this heat generation step of step S4, the second active material 42 is mainly utilized. In addition, in this embodiment, the heat generation step is performed in an SOC region where the SOC value of the secondary battery 2 is 70% or higher.

[0046] Furthermore, by performing the heat generation step of step S4, the internal resistance of the secondary battery 2 decreases as the temperature of the secondary battery 2 increases, as shown in FIG. 8. Then, in step S5 after the heat generation step, high-rate discharge is performed while the internal resistance of the secondary battery 2 is low, as shown in FIG. 6. This enables high-power discharge of the secondary battery 2. Then, in the high-power step of step S5, the motor is driven by high-rate discharge of the secondary battery 2, and the electric flying vehicle 100 rises to a predetermined altitude. Also, in the high-power step of step S5, the secondary battery 2 outputs power in a first high utilization region where the utilization rate of the first active material 41 is higher than the utilization rate of the second active material 42. Then, in the high-power step, the first active material 41 is mainly utilized. Furthermore, the high-power step is performed in a region where the resistance of the first active material 41 is lower than the resistance of the second active material 42.

[0047] In steps S3 to S5, from the start of high-rate discharge until the electric flying body 100 reaches the normal operation start point, the secondary battery 2 is required to continuously provide high output. In other words, from steps S3 to S5, the secondary battery 2 continuously performs high-rate discharge. In this embodiment, the time for high-rate discharge is shorter than the time for discharge during normal operation. In other words, at takeoff at startup, the time for continuous high-rate discharge of the secondary battery 2 is shorter than the time for normal operation. In this embodiment, the normal operation start point refers to the altitude at which normal operation starts. Furthermore, startup refers to the period from when the electric flying body 100, which is the electric vehicle 10, starts moving until normal operation begins.

[0048] After the electric flying body 100 reaches the normal operation start point in step S5, the battery control unit 3 controls the discharge of the secondary battery 2 in step S6 to cruise the electric flying body 100 through normal operation up to the destination point. The normal operation of the electric flying body 100 involves movement mainly along the horizontal direction, so the amount of power required is significantly less than the amount of power required for takeoff at startup, as shown in FIG. 7. Furthermore, during normal operation, the internal resistance of the secondary battery 2 tends to be lower than during the heat generation step, as shown in FIG. 8. Therefore, the temperature of the secondary battery 2 gradually decreases. During normal discharge, which is the discharge of the secondary battery 2 during normal operation, the discharge rate can be, for example, 0.3 to 1.0 C.

[0049] 6, steps after step S6 are omitted. In step S6, the electric flying object 100 is operated normally up to the destination, then the electric flying object 100 is descended from a predetermined altitude to a landing point and landed. Landing requires a higher output than normal operation. Therefore, when landing the electric flying object 100, the battery control unit 3 controls the secondary battery 2 to discharge at a high rate.

[0050] Next, the effects of this embodiment will be described. In the battery system 1, the secondary battery 2 is configured such that, when high-rate discharge is performed at startup, the utilization rate of the second active material 42 becomes higher than the utilization rate of the first active material 41, and then the utilization rate of the first active material 41 becomes higher than the utilization rate of the second active material 42. Therefore, at startup, the temperature of the secondary battery 2 is increased, thereby reducing the internal resistance of the secondary battery 2 and allowing high-rate discharge of the secondary battery 2. In other words, by suppressing temporary deterioration of the secondary battery 2, high output power of the secondary battery 2 can be ensured. As a result, output power at startup of the electric vehicle can be improved.

[0051] Generally, electric aircraft require high power output during takeoff. Therefore, high-rate discharge of the secondary battery is performed during takeoff. Assume an electric aircraft that does not perform a heat generation step before the high-power step. In this case, high-rate discharge may cause a bias in the lithium ion concentration distribution in the secondary battery during takeoff. If a bias in the lithium ion concentration distribution occurs, discharge may be limited even if the secondary battery's SOC is sufficiently high, potentially resulting in temporary deterioration of the secondary battery. Therefore, the battery system 1 of this embodiment is controlled to perform a heat generation step before the high-power step. Specifically, during start-up, a high-rate discharge region that serves as a high-resistance region and a second high-utilization region is intentionally established in the high-rate discharge region, thereby increasing the temperature of the secondary battery 2. This facilitates lithium ion movement in the secondary battery 2, reducing the likelihood of a bias in the lithium ion concentration distribution. As a result, temporary deterioration of the secondary battery 2 can be suppressed, and the high-power step can be performed while the internal resistance of the secondary battery 2 is sufficiently low. Furthermore, in the high-power step after the heat generation step, the utilization rate of the first active material 41 is higher than that of the second active material 42. Furthermore, in the SOC region where the high-power step is performed, the resistance of the first active material 41 is likely to be lower than the resistance of the second active material 42. This makes it possible to reliably ensure high power output of the secondary battery 2. As a result, it is possible to improve the output performance throughout the entire period during which high-rate discharge is performed.

[0052] Next, this embodiment will be described in comparison with Comparative Embodiment 1. In this embodiment, the secondary battery 2 contains both a first active material 41 and a second active material 42 in the active material layer 40 of the positive electrode 4. Therefore, as shown in FIG. 8 , compared to Comparative Embodiment 1, which contains only lithium nickel cobalt manganese oxide as the positive electrode active material, this embodiment, which includes the second active material 42, can increase the internal resistance of the secondary battery 2 in the SOC region where the heat generation step is performed. This allows the temperature of the secondary battery 2 to be reliably increased, and the internal resistance of the secondary battery 2 to be reliably reduced in the SOC region where the high-power step after the heat generation step is performed. In other words, in this embodiment, the temperature of the secondary battery 2 can be increased when high power output is required, and the utilization rate of the low-resistance first active material 41 can be increased. As a result, high power output can be ensured while significantly reducing the internal resistance of the secondary battery 2.

[0053] In general, when secondary batteries are used as a battery module, depending on how multiple secondary batteries are restrained using restraining members, the electrolyte may be pushed out of the electrodes, resulting in a decrease in the amount of electrolyte in the electrodes. In such cases, temporary deterioration of the secondary battery due to high-rate discharge may be more likely to occur. Furthermore, if so-called electrode swelling occurs due to a change in the volume of the active material, temporary deterioration of the secondary battery due to high-rate discharge may also be more likely to occur. In contrast, in this embodiment, the high-power step is performed after the heat generation step. Therefore, even if the electrolyte is pushed out of the electrodes due to restraint of the secondary battery 2, temporary deterioration of the secondary battery 2 is easily suppressed. As a result, high power output of the secondary battery 2 can be reliably ensured.

[0054] The resistance of the first active material 41 decreases as the SOC of the secondary battery 2 increases. Therefore, in the SOC region where the high power step is performed, the resistance of the first active material 41 tends to become even smaller. Therefore, in the high power step where the utilization rate of the first active material 41 is high, the high power output of the secondary battery 2 can be further ensured.

[0055] The proportion of the first active material 41 relative to the total active material of the positive electrode 4 is 50 to 95 wt %, and the proportion of the second active material 42 relative to the total active material of the positive electrode 4 is 5 to 50 wt %. Therefore, by adjusting the content ratio of the first active material 41 and the second active material 42 in the positive electrode 4 within the above range, the range of SOC that becomes the second high utilization region can be adjusted. Therefore, any SOC region where the heat generation step is to be performed can be adjusted to become the second high utilization region. As a result, the heat generation step can be performed for an appropriate period of time in accordance with any starting SOC value.

[0056] When the initial SOC value is relatively high, the ratio of the first active material 41 to the total active materials of the positive electrode 4 is preferably 80 to 95 wt %, and the ratio of the second active material 42 to the total active materials of the positive electrode 4 is preferably 5 to 20 wt %. In this case, the heat generation step and the high-power step can be performed efficiently. That is, when the initial SOC value is relatively high, if the ratio of the second active material 42 is higher than the above ratio, the heat generation step may be too long, and the heat generation step and the high-power step may not be performed efficiently. Furthermore, if the ratio of the second active material 42 to the total active materials of the positive electrode 4 is lower than the above ratio, the heat generation step may not be performed sufficiently. Therefore, when the initial SOC value is relatively high, the ratio of the second active material 42 to the total active materials of the positive electrode 4 is preferably 5 to 20 wt %. This allows the heat generation step and the high-power step to be performed efficiently. Furthermore, if the proportion of the first active material 41 is higher than the above proportion, the proportion of the second active material 42 may be too low when the initial SOC value is relatively high, and the heat generation step may not be performed sufficiently. Furthermore, if the proportion of the first active material 41 is lower than the above proportion, the proportion of the second active material 42 may be too high when the initial SOC value is relatively high. Therefore, when the initial SOC value is relatively high, the proportion of the first active material 41 relative to the total active material of the positive electrode 4 is preferably 80 to 95 wt %. In this case, the heat generation step and the high-power step can be performed efficiently. As a result, the output at startup can be further improved.

[0057] Furthermore, when the starting SOC value is set to a relatively low value, the ratio of the second active material 42 to the total active materials of the positive electrode 4 is preferably 40 to 50 wt %, and the ratio of the first active material 41 to the total active materials of the positive electrode 4 is preferably 50 to 60 wt %. In this case, when the starting SOC value is relatively low, the heat generation step and the high-power step can be carried out efficiently.

[0058] When the initial SOC value is relatively high, the ratio of the second active material 42 to the total active material of the positive electrode 4 is preferably 10% by weight or less. In this case, the heat generation step and the high-power step can be performed reliably and efficiently. Furthermore, when the initial SOC value is relatively high, the ratio of the second active material 42 to the total active material of the positive electrode 4 is preferably 9% by weight or less. In this case, the heat generation step and the high-power step can be performed even more reliably and efficiently.

[0059] The first active material 41 is a lithium nickel cobalt manganese oxide having a layered rock salt structure. The second active material 42 is a lithium manganese iron phosphate having an olivine structure. Therefore, the heat generation step and the high-power step can be reliably and efficiently performed. As a result, temporary deterioration of the secondary battery 2 can be reliably suppressed and high power can be reliably ensured. Furthermore, a second high utilization region can be easily established in both the high-rate discharge region and the low SOC region at startup. Furthermore, a high-resistance region can be easily established in the high-rate discharge region at startup, and the second active material 42 is likely to have a region with lower resistance than the first active material 41 in the low SOC region. Therefore, the heat generation step can be reliably performed in the high-rate discharge region at startup, and high power can be reliably ensured in the low SOC region. As a result, high power can be reliably ensured in the secondary battery 2 during both takeoff and landing.

[0060] Furthermore, the lithium manganese iron phosphate of the second active material 42 is less susceptible to particle cracking and surface deterioration than the lithium nickel cobalt manganese oxide of the first active material 41. This improves the durability of the secondary battery 2. As a result, the life of the secondary battery 2 can be extended.

[0061] In this embodiment, the average particle diameter of the first active material 41 is larger than the average particle diameter of the second active material 42. This reliably suppresses deterioration of the first active material 41. Specifically, the first active material 41 reacts more readily with the electrolyte 20 on its surface than the second active material 42. This reaction may result in the formation of a coating on the surface of the first active material 41, which may cause deterioration of the first active material 41. Therefore, in this embodiment, the average particle diameter of the first active material 41 is larger than the average particle diameter of the second active material 42. This reduces the overall surface area of ​​the first active material 41 contained in the positive electrode 4. This reduces the overall surface area of ​​the first active material 41 that contacts the electrolyte 20. This suppresses the reaction between the first active material 41 and the electrolyte 20, reliably suppressing deterioration of the first active material 41. As a result, the life of the secondary battery 2 can be extended.

[0062] The average particle diameter of the second active material 42 is smaller than the average particle diameter of the first active material 41. This further reduces particle cracking of the second active material 42, thereby ensuring a longer lifespan of the secondary battery 2 and preventing temporary deterioration of the secondary battery 2. Furthermore, the smaller the average particle diameter of the second active material 42, the easier it is to reduce the resistance of the second active material 42 and to more uniformly distribute the second active material 42 in the positive electrode 4, thereby improving the safety of the secondary battery 2. However, if the particle diameter of the second active material 42 is reduced to nanometers (less than 100 nm), the particles of the second active material 42 tend to aggregate, making it difficult to uniformly mix the first active material 41 and the second active material 42. Therefore, it is preferable that the particle diameter of the second active material 42 be 100 nm or greater. This improves manufacturability.

[0063] In the low SOC region, the second active material 42 has a lower resistance than the first active material 41. The secondary battery 2 is also configured to have a second high utilization region in the low SOC region. This further ensures high output from the secondary battery 2 when the electric flying vehicle 100 lands in the second high utilization region of the low SOC region. As a result, the output at the start of the electric vehicle 10 can be further improved.

[0064] The electric flying object 100 includes the battery system 1. Therefore, when the electric flying object 100 starts, temporary deterioration of the secondary battery 2 is suppressed, thereby ensuring high output.

[0065] The electric flying object 100 includes a secondary battery. Therefore, when the electric flying object 100 starts, temporary deterioration of the secondary battery 2 is suppressed, thereby ensuring high output.

[0066] As described above, according to this embodiment, it is possible to provide the battery system 1, the secondary battery 2, and the electric flying body 100 that can improve the output of the electric vehicle 10 when it is started.

[0067] (Experimental Example 1) In this example, discharge tests and cycle tests were carried out using a plurality of secondary batteries having the same basic structure as in the first embodiment but with different compositions of the positive electrode active material. 0.8 Co 0.1 Mn 0.1 O2 (hereinafter simply referred to as "NCM") and LiMn 0.6 Fe 0.4PO4 (hereinafter simply referred to as "LMFP") was used, and graphite was used as the negative electrode active material. The electrolyte was a solvent containing vinylene carbonate and 1M LiPF6. Vinylene carbonate was added so that it accounted for 1% of the total electrolyte. The electrolyte solvent was a mixture of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a volume ratio of 1:1:1. FIG. 9 is a photograph of the cross section of the secondary battery of Example 1 in Table 1, which will be described later, observed with a scanning electron microscope.

[0068] The discharge test conditions were an ambient temperature of 25°C, a secondary battery SOC of 90% at the start of discharge, a discharge rate of 10C, and a lower limit voltage of 2.8V. The discharge test measured the current flow time, which is the time from the start of discharge until the discharge voltage reached the lower limit and the secondary battery stopped discharging. The cycle test conditions were an ambient temperature of 25°C, a charge / discharge voltage of 2.8 to 4.2V, and a discharge rate of 1C. The cycle test measured the capacity retention of the secondary battery after 300 charge / discharge cycles. The capacity retention is the ratio of the discharge capacity after the test to the discharge capacity before the test.

[0069] In this discharge test, a current-carrying time of 230 seconds or more is set as the standard for improving the output of an electric flying vehicle at startup when using a secondary battery in the vehicle. Furthermore, a current-carrying time of 240 seconds or more is set as the standard for further improving the output of an electric flying vehicle at startup. Based on the test results, the ratio of NCMs and LMFPs that met this standard was determined. Table 1 below indicates a current-carrying time of 230 seconds or more as "○," a current-carrying time of 240 seconds or more as "◎," and a current-carrying time of less than 230 seconds as "×."

[0070] In this cycle test, a capacity retention rate of 80% or more was set as the standard for adequately suppressing deterioration of the secondary battery. Therefore, the ratio of NCM to LMFP that met this standard was determined from the test results. In Table 1 below, a capacity retention rate of 80% or more is indicated by "○," and a capacity retention rate of less than 80% is indicated by "×."

[0071] The results of the discharge test and cycle test are shown in Table 1 below. The item "active material ratio" in Table 1 below indicates the weight ratio of NCM or LMFP to the total active material of the positive electrode. Also, the maximum temperature in Table 1 below indicates the temperature at which the secondary battery reached its highest temperature during the discharge test.

[0072] [Table 1]

[0073] As shown in Table 1 above, in the discharge test, Comparative Examples 1 and 2 did not meet the above criteria, whereas Examples 1 to 3 had a current-flow time of 230 seconds or more, satisfying the criteria. Here, Examples 1 to 3 had a higher maximum temperature than Comparative Example 1. From these results, it is believed that Examples 1 to 3, containing LMFP as the positive electrode active material, were able to reliably perform the heat generation step during high-rate discharge. Therefore, it is believed that the internal resistance of the secondary battery could be reduced, and high-rate discharge could be efficiently performed using NCM. As a result, it is believed that the current-flow time could be relatively long. Furthermore, Examples 1 to 3 had a longer current-flow time than Comparative Example 2. From this, it is believed that by containing LMFP at a ratio of 20% or less of the total positive electrode active material, the period during which the heat generation step was performed was prevented from becoming too long when the SOC value at the start of discharge was relatively high, and long-term discharge was possible with the secondary battery's internal resistance sufficiently low. Furthermore, Examples 1 to 3 contained NCM, which has a high energy density, in the positive electrode. Therefore, it is believed that the inclusion of NCM in Examples 1 to 3 enabled a relatively long current-carrying time. Furthermore, in Example 2, the current-carrying time was 240 seconds or more, which was longer than those of Examples 1 and 3. Here, Example 2 contains LMFP at a ratio of more than 5% and 10% or less of the total positive electrode active material. Therefore, it is believed that the heat-generating step could be performed for a more efficient period. In other words, it is believed that the temperature of the secondary battery was sufficiently increased by the heat-generating step, while the period of the heat-generating step was shortened, allowing for discharge. As a result, it is believed that the high output of the secondary battery 2 could be maintained for a relatively long period, and the current-carrying time could be extended. On the other hand, Comparative Example 1 uses NCM, which has a high energy density, as the positive electrode active material, but does not contain LMPF. Therefore, it is believed that the secondary battery was not able to generate heat sufficiently, and the internal resistance of the secondary battery was not able to be sufficiently reduced. Therefore, it is believed that Comparative Example 1 did not satisfy the above criteria. Furthermore, Comparative Example 2 contains only LMPF as the positive electrode active material.Therefore, in Comparative Example 2, the heating step was performed for too long a period of time, and the current application time was shortened because NCM was not contained. As a result, the above criteria could not be met.

[0074] Furthermore, as shown in Table 1 above, in the cycle test, Examples 1 to 3 and Comparative Example 2 showed a capacity retention rate of 80% or more, satisfying the above criteria. Here, LMPF is less susceptible to particle cracking and surface deterioration due to charge / discharge compared to NCM. Therefore, it is believed that Examples 1 to 3 and Comparative Example 2, which contain LMPF as the positive electrode active material, showed high capacity retention rates. On the other hand, Comparative Example 1, which does not contain LMPF as the positive electrode active material, showed a capacity retention rate of less than 80%, failing to satisfy the above criteria.

[0075] The present invention is not limited to the above-described embodiments, and can be applied to various embodiments within the scope of the present invention.

[0076] <Other> The features of the present invention are as follows. [Section 1] A battery system (1) mounted on an electric vehicle (10), A secondary battery (2); a battery control unit (3) that controls the discharge of the secondary battery, the battery control unit controls the secondary battery to perform high-rate discharge, which is discharge at a higher rate than the discharge rate of the secondary battery during normal operation of the electric vehicle, at the start of the electric vehicle; the positive electrode (4) of the secondary battery comprises a first active material (41) and a second active material (42) having a high resistance region in which resistance is higher than that of the first active material in a high rate discharge region which is an SOC region of the secondary battery in which the high rate discharge is performed at the start-up; The secondary battery is configured such that, when the high-rate discharge is performed at the time of startup, the utilization rate of the second active material becomes higher than the utilization rate of the first active material, and then the utilization rate of the first active material becomes higher than the utilization rate of the second active material. [Section 2] Item 2. The battery system according to item 1, wherein the first active material has a smaller resistance as the SOC of the secondary battery increases. [Section 3] Item 3. The battery system according to item 1 or 2, wherein the ratio of the first active material to the total active material of the positive electrode is 50 to 95 wt %, and the ratio of the second active material to the total active material of the positive electrode is 5 to 50 wt %. [Section 4] Item 4. The battery system according to any one of Items 1 to 3, wherein the first active material is a lithium nickel cobalt manganese oxide having a layered rock salt structure, and the second active material is lithium manganese iron phosphate having an olivine structure. [Section 5] A secondary battery (2) mounted on an electric flying object (100) and having a positive electrode (4) and a negative electrode (5), the positive electrode comprises a first active material (41) and a second active material (42) having a higher resistance than the first active material when the secondary battery has a predetermined SOC value; A secondary battery, wherein the first active material is a lithium nickel cobalt manganese oxide having a layered rock salt structure, and the second active material is lithium manganese iron phosphate having an olivine structure. [Section 6] Item 6. The secondary battery according to Item 5, wherein in a low SOC region where the SOC value of the secondary battery is lower than a predetermined value, the second active material has a lower resistance than the first active material, and the secondary battery is configured to have a second high utilization region in the low SOC region where the utilization rate of the second active material is higher than the utilization rate of the first active material. [Section 7] An electric flying object (100) comprising the battery system according to any one of items 1 to 4. [Section 8] Item 7. An electric flying object comprising the secondary battery according to item 5 or 6. [Explanation of symbols]

[0077] 1... battery system, 2... secondary battery, 3... battery control unit, 4... positive electrode, 10... electrically driven mobile body, 41... first active material, 42... second active material

Claims

1. A secondary battery (2) having a positive electrode (4) and a negative electrode (5), The positive electrode has a first active material (41) and a second active material (42), The first active material is a lithium nickel cobalt manganese oxide represented by the following formula (1), and the second active material is lithium manganese iron phosphate, the average particle size of the first active material is larger than the average particle size of the second active material; The secondary battery is mounted on an electric flying object (100), In the following formula (1), x + y + z = 1, 0.6≦x<1, The secondary battery further comprises a solid electrolyte, The secondary battery, wherein the solid electrolyte is an oxide-based solid electrolyte having a pyrochlore structure and containing at least lithium, lanthanum, niobium, oxygen, and fluorine. L)) ｘ Co ｙ Mn ｚ O ２ ・・・(1)

2. 2. The secondary battery according to claim 1, wherein in the formula (1), 0.02≦y≦0.2 and 0.02≦z≦0.

2.

3. The second active material, lithium manganese iron phosphate, is represented by the following formula (3): The secondary battery according to claim 1 or 2, wherein in the following formula (3), 0.5<x≦0.6: LiMn ｘ Fe １－ｘ PO ４ ・・・(3)

4. A secondary battery (2) having a positive electrode (4) and a negative electrode (5), The positive electrode has a first active material (41) and a second active material (42), The first active material is lithium nickel cobalt manganese oxide, and the second active material is lithium manganese iron phosphate represented by the following formula (3): the average particle size of the first active material is larger than the average particle size of the second active material; The secondary battery is mounted on an electric flying object (100), In the following formula (3), 0.5<x≦0.6, The secondary battery further comprises a solid electrolyte, The secondary battery, wherein the solid electrolyte is an oxide-based solid electrolyte having a pyrochlore structure and containing at least lithium, lanthanum, niobium, oxygen, and fluorine. LiMn ｘ Fe １－ｘ PO ４ ・・・(3)

5. 5. The secondary battery according to claim 1, wherein the first active material has a resistance that decreases as the State Of Charge value of the secondary battery increases.

6. 5. The secondary battery according to claim 1, wherein the ratio of the first active material to the total active material of the positive electrode is 50 to 95% by weight, and the ratio of the second active material to the total active material of the positive electrode is 5 to 50% by weight.

7. 7. The secondary battery according to claim 6, wherein a ratio of the first active material to the total active material of the positive electrode is 80 to 95% by weight, and a ratio of the second active material to the total active material of the positive electrode is 5 to 20% by weight.

8. 5. The secondary battery according to claim 1, wherein the ratio of the first active material to the total active material of the positive electrode is 90% by weight or more, and the ratio of the second active material to the total active material of the positive electrode is 10% by weight or less.

9. 5. The secondary battery according to claim 1, wherein the secondary battery is configured to have a second high utilization region in which a utilization rate of the second active material is higher than a utilization rate of the first active material in an SOC region where a State Of Charge value of the secondary battery is equal to or higher than a specific value.

10. 10. The secondary battery according to claim 9, wherein the specific value is 70%.

11. 11. The secondary battery according to claim 10, wherein the second high utilization region is present when the State Of Charge value of the secondary battery is in the range of 80 to 90%.

12. 5. The secondary battery according to claim 1, wherein the secondary battery is configured to have a second high utilization region in which a utilization rate of the second active material is higher than a utilization rate of the first active material in a low SOC region in which a State Of Charge value of the secondary battery is lower than a predetermined value.

13. The secondary battery according to claim 12 , wherein the low SOC region is a region where the State Of Charge value is 30% or less.

14. The secondary battery according to claim 13 , wherein when the State of Charge value is 10%, the utilization rate of the second active material is higher than the utilization rate of the first active material.

15. the secondary battery has a first high utilization region in which the utilization rate of the first active material is higher than the utilization rate of the second active material in a region in which the State Of Charge value is in the range of 0 to 100%, and two second high utilization regions in which the utilization rate of the second active material is higher than the utilization rate of the first active material; The secondary battery according to claim 1 or 4, wherein the first high utilization region is sandwiched between two of the second high utilization regions.

16. The secondary battery according to claim 1 or 4, wherein the positive electrode contains at least one of a conductive material and a binder.

17. 5. The secondary battery according to claim 1, wherein the negative electrode has, as an active material, at least one of graphite, silicon, lithium metal, and lithium titanate-based active materials.

18. 5. The secondary battery according to claim 1, further comprising an electrolyte, the electrolyte being impregnated in each of the positive electrode and the negative electrode, and containing a non-aqueous solvent and a lithium salt.

19. The secondary battery according to claim 1 or 4, further comprising a separator disposed between the positive electrode and the negative electrode, the separator having lithium ion permeability.

Images